The instantly disclosed invention relates generally to a method of cutting steel; and, more particularly, to a method of torch cutting slab, bloom or billet steel. Slab steel is produced by the continuous casting method. Continuous casting is the process whereby molten steel is solidified into semi-finished billets, blooms or slabs for subsequent rolling in the finishing mills.
The continuous casting process begins by pouring steel from an electric or oxygen furnace into a ladle. The ladle is raised on to a turret that rotates the ladle into the casting position above a tundish. Liquid steel flows out of the ladle, into the tundish and then into a water-cooled copper mold. Solidification begins in the mold and continues through the forming process. Finally, the billet, bloom or slab is torch or machine-cut, discharged and stored for further processing.
It is during the torch cutting stage of the casting process that the instantly disclosed method contributes to the efficiency of the process and the quality of the finished product. Near the end of the casting process, the slab, bloom or billet is cooled, straightened and transferred on roller tables to a cut-off machine, which cuts the product into ordered lengths. This cutting is typically effected by torches. And torches, in the slab, bloom or billet casting process, are typically fueled by oxygen and a fuel gas. Fuel gasses are frequently hydrocarbons, such as natural gas (methane). Natural gas is a commonly employed fuel gas because it does an adequate job, it""s readily available and it""s relatively inexpensive.
The primary objective of this invention is to provide an improved fuel gas to replace methane so that the torch will generate a hotter flame, thus producing a narrower, quicker and cleaner cut. Other patent disclosures have suggested a variety of additives to be added to a hydrocarbon fuel gas to provide an alleged improvement in the cutting process, but none has disclosed the use of propylene to the exclusion of other hydrocarbons in the quantities or pressures suggested herein. U.S. Pat. No. 5,380,346, which issued Jan. 10, 1995 to Fritz, teaches that a fortified torch gas can be formulated from a mixture of a hydrocarbon base gas (LPG, and possibly propylene) and an additive selected from the group consisting of variety of ethers, aldehydes, ketones, glycols and alcohols. This patent also provides an elaborate discussion of the prior art relative to cutting fuels.
U.S. Pat. No. 5,922,144, which issued Jul. 13, 1999 to Sykes, discloses a method for expediting the cutting of steel, especially as the cutting relates to salvaging scrap steel from retired ships. The method involves the use of a combustion enhancing gas, typically oxygen, set at a level of 150 to 220 pounds per square inch (psi) and a combustible gas, such as propane, chemtane, propylene, Mapp or natural gas at 35 to 80 psi. It is alleged that this particular fuel mixture and method allows the operator to cut metal at a faster rate, typically 5 to 8 times as fast as conventional methods.
But, notwithstanding the teachings of the prior art, there remains a need for an improved method to enhance the speed and effectiveness of cutting slab, bloom and billet steel produced in the continuous casting process. This need is met by a method which comprises positioning a cutting torch to cut slab, bloom and billet steel into manageable dimensions; and, fueling said torch with propylene and oxygen and wherein said torch has a tip for delivering and blending said propylene with oxygen on a predetermined cutting line on the surface of said slab, and wherein the oxygen is delivered to the cutting surface of the slab steel at between 30 and 50 psi and the propylene is delivered to the cutting surface at between 5 and 25 psi.